Purification of petroleum coke



Nov. 26,v las/7 LE Rol E. HuTcHlNGs PURIFICATION OF PETROLEUM COKE FiledMay 10, 1956` United States Patent PURIFICATION OF PETROLEUM COKE Le RoiE. Hutchings, Crystal Lake, Ill., assignor to The Pure Oil Company,Chicago, Ill., a corporation of Ohio Application May 10, 1956, SerialNo. 584,059

3 Claims. (Cl. 202-31) This invention relates to a method of purifyingpetroleum coke and, more particularly, to the removal of Sulfur andnitrogen compounds from petroleum coke by hydrogenation at temperaturesof at least about 900 F. and pressures greater than 1000 p. s. i. g.

Naturally occurring sulfur and nitrogen compounds found in petroleumcoke are known to have a deleterious effect when the coke is used incertain applications such as metallurgie electrodes. For this reason itis desirable that the sulfur compounds and nitrogen compounds beremoved. However, little is known as to the form in which sulfur existsin petroleum coke, but there is evidence to show that compounds such asmercaptans, suldes, thiophanes, thiophenes and disuldes are the productsof the decomposition of different high molecular weight sulfur compoundsoriginally present in the crude oil. The amount and kinds of sulfurcompounds present in petroleum coke depend upon the amount of totalsulfur in the asphalt from which the coke is prepared and the manner ofits preparation. When asphalt is converted to coke there is a generaldegradation of the majority of sulfur compounds with the evolution ofhydrogen sulfide, leaving a residual quantity of sulfur and nitrogencompounds which is diicult to remove and is highly undesirable as far asthe end characteristics of the coke are concerned. Numerous methods havebeen proposed for the production of low sulfur, solid carbonaceousfuels. In general, many of these methods relate to coal desulfurizationand the principal problem is sulfur removal without excessive conversionof the coal into gas or vapor. Furthermore, the pressures andtemperatures used are not sufficient for the treatment of petroleum cokeand these processes are concerned with the preparation of a non-cokeproduct. In addition, these processes directed to the desulfurization ofcoal do not effect a sucient reduction in the sulfur and nitrogencontent to vbe effective for use in petroleum coke desulfurization.

It is reported in the prior art that coke may be desulfurized by the useof a catalyst and through treatment at temperatures ranging from 1340"to 1600 F., using oxidizing, reducing or inert atmospheres. Suchmaterials as nitrogen, carbon 4dioxide, carbon monoxide, methane,ethylene water gas, anhydrous ammonia, and hydrogen have been used andstudied in connection with sulfur reduction. It has been reported thathydrocarbon gases are most eicient in this respect. However, carbon isformed from these gases and interferes with subsequent sulfurdeterminations. I have been unable to reproduce the data reported in theart except when samples known to be contaminated with such outsidecarbon have been analyzed. Several other investigators concerned withthe use of various atmospheres for the reduction of sulfur in petroleumcoke have concluded that the presence or absence of an oxidizing orreducing atmosphere does not influence the reaction one `way or theother.

In accordance with the present invention, it has been found thatpetroleum coke can be elfectively desulfurized by the use of hydrogen atrelatively low temperatures and under high pressure. I have foundfurther that the other desulfurizing atmospheres described in the priorart are ineffective. For example, ethylene when used at atmosphericpressure and temperatures of about l700 F. is an ineffectivedesulfurizing atmosphere. The same may be said for oxygen and the othergases enumerated when used at pressures under atmospheric pressure andunder conditions of elevated temperature. It has been found that thegreatest amount of desulfurization per unit of time takes place when thecoke is subjected to high hydrogen pressures of at least 1000 lbs. persquare inch at the reaction temperature, While the coke is maintained attemperatures of at least about 900 F. and preferably about 1000 F. Thedegree of removal of sulfur and other compounds is directly related tothe temperature, the hydrogen pressure and the Contact time. A furtheradvantage of the invention is that in addition to reducing the sulfurand nitrogen contents, the present process yields hydrocarbon liquids,gases, semi-liquids, or highly viscous fluids and ammonia asby-products. If the higher temperatures disclosed in the prior art wereused, many of these valuable compounds would be destroyed. The processis also effective for the removal of water and volatile materialsoriginally present in the coke. Accordingly, a primary object of theinvention isY to provide a process for the removal of `sulfur compoundsfrom petroleum coke by high pressure hydrogenation at temperatures of atleast 900v F.

A second object of the invention is to provide a process for the removalof sulfur compounds and nitrogen compounds from petroleum coke bytreatment with hydrogen at temperatures between about 900 F. and 1050 F.using hydrogen pressures of at least 1000 lbs. per square inch at thereaction temperatures.

A further object of the invention is to provide a process for preparingcoke for use in the manufacture of metallurgie electrodes which containsa certain minimum amount of sulfur compounds. v

These and further objects of the invention will be described or becomeapparent as the description thereof proceeds.

The drawing is a simplified schematic flow diagram `that may be used toillustrate the process.

.chamber 6. The residencetime in the reaction vchamber 6 may vary fromless than 1 hour to several hours, depending on the temperature anddegree of desulfurization desired. The reaction chamber is Wellinsulated and all heat is supplied by the circulating gases from line 8.The gases and reaction products pass out through the top of the reactorvia line 11 and to condenser 12, which is operated at about atmosphericor elevated pressure and at about 500 F. If desired, a dust separator(not shown) may be provided within line 11 to separate any cokeparticles that may be carried over and return same to the reactor. Waxyand resinous materials are removed in condenser 12 as indicated at line13. The gases from condenser 12 pass via line 14 to Warm condenser 15,which is operated at about 212 F. for the removal of any heavy liquidproducts at line 16.` 'Ihe remaining gaseous products pass through line17 to cold condenser 18 operated at normal cooling water temperatures.Condenser 18 may be refrigerated to recover light liquids and a watersolution of NH3 and H28, which pass via line 19 `to separator 20 whereinthe water solubles collect as a lower phase and the light liquids as anupper phase. Additional water may be used to scrub these gases. Thewater solubles are collected through line 21 and the light liquid atline 22. The remaining gases, comprising principally hydrogen, are drawnol at line 23 for recycle via line 24 through compressor 25 and line 26to furnace 7.` Part of the oil-gases may be discarded via line 27 toprevent a build-up of inerts and methane. Additional hydrogen is addedvia makeup H2 line 28. In the furnace the gases are heated to thedesired temperature, i.\e., about 1200 F. The amount of gas recirculateddepends upon the heat losses, but in general will be about 4,000 s. c.f. per 100 pounds of coke. The temperature of the gases leaving reactionchamber 6 should be at least about 700 F. to prevent deposition of theheavier components` therefrom.

In order to demonstrate the invention, a series of experiments was`conducted wherein a petroleum coke was treated under various reactionconditions. The coke used in these experiments was largely from a sourcrude obtained by coking a reduced crude in a normal refinery processingoperation. Samples were ground to 100 mesh and iiner and treated withhydrogen in a rocking autoclave. The conditions were adjusted so thatthe time in minutes at which each sample was held at a particulartemperature could be recorded. The results are shown in the followingtable:

Table Run No Feed 1 2 3 4 5 Time (min.) at:

Time, total, mmm- 140 205 285 490 225 Max. press., p. s. i. g.. i, 1752,650 2, 475 2, 440 2,350 Sulfur, wt. percent--- 2.88 2. 88 1. 0.850. 1. 30 Nitrogen, wt. percent 1. 28 1.05

The pressure in the autoclave rose to the indicated maximum pressuresduring heating and then gradually decreased as hydrogen was consumed inthe reaction. Inrun #4, of the grams of coke charged, containing 2.88%sulfur, about 15.6 grams of product were recovered which contained 0.53weight percent of sulfur. This reduction was effected by the consumptionof 2.8 grams of hydrogen at about 1000 F. and 2440 lbs. per square inchpressure for a total reaction time above 800 F. of 490 minutes. Thisrepresented the best product that was obtained. It will be observed fromthe foregoing experiments that, contrary to the prior art, lowtemperatures and very high pressures do effect a reduction of the sulfurcontent. It is apparent from the f t 4 experiments that the longer thecoke is maintained at temperatures between about 1000 to 1015 F. thegreater will be the desulfurization, provided the pressure is suicientlyhigh, that is, at least about 1000 p. s. i. g. and preferably over 2000p. s. i. g.

In carrying out the process of the invention, it is only necessary tobring the coke into intimate contact with an atmosphere containing atleast about 10% by weight of hydrogen per unit weight of charge underconditions such that the coke and hydrogen are contacted at temperaturesof at least about 800 F. to as high as 1050 F. within a reaction zone ata pressure of at least about 1000 lbs. per square inch at the reactiontemperature. The coke may be grounded or pulverized into a granular orfinely divided form and passed into the top of a reaction zone. Hydrogenunder pressure and preheated to a temperature of about 900 to 1100 F. isintroduced into the reaction zone at the bottom or at a plurality ofpoints therein. The reaction zone may be fitted with independent meansfor bringing the coke to the reaction temperatures. The reaction, onceunder way, is endothermic, and heat must be supplied to maintain thereaction temperature and pressure. The desulfurized coke may be removedfrom the bottom of the reaction zone and passed to a cooling zone andthen to conveyors for storage. The process may be carried out batchwiseor in a continuous manner, using in the rst instance a static bed and inthe latter a homogeneous or tluidized bed of coke in the reactor. Oneadvantage of the process using high pressures is that it is amenable tocontinuous and cyclic ow of reactants through the reactor which makesindustrial application economically attractive.

What is claimed is:

1. The method of desulfurizing petroleum coke containing about 3 Weightpercent of sulfur which comprises subjecting said coke to hydrogenationat a temperature between about 900 F. to 1050 F. in the presence of atleast about 10 weight percent of hydrogen per unit weight of said cokeand maintaining said reaction at a temperature of about 985 F. to 1015F. for a period of time ranging from about 2 hours to 6.5 hours at apressure between about 2000 p. s. i. g. to 3000 p. s. i. g. during saidreaction and recovering a desulfurized petroleum coke having a sulfurcontent of about 1.3 weight percent of sulfur or less.

2. The method in accordance with claim 1 in which said reaction ismaintained at a temperature of 985 to l0l5 F. and a pressure of about2475 p. s. i. g. for at least about 3 hours and a petroleum coke havinga sulfur content of about 0.85 weight percent is recovered.

`3. The method in accordance with claim 1 in which said reaction ismaintained at a temperature of 985 to 1015 F. at a pressure of about2440 p. s. i. g. for at least about 6.5 hours and a petroleum cokehaving a sulfur content of about 0.53 weight percent is recovered.

McKinley et al. Dec. 6, 1955 Iahnig Apr. 24, 1956

1. THE METHOD OF DESULFURIZING PETROLEUM COKE CONTAINING ABOUT 3 WEIGHTPERCENT OF SULFUR WHICH COMPRISES SUBJECTING SAID COKE TO HYDROGENATIONAT A TEMPERATURE BETWEEN ABOUT 900*F. TO 1050*F. IN THE PRESENCE OF ATLEAST ABOUT 10 WEIGHT PERCENT OF HYDROGEN PER UNIT WEIGTH OF SAID COKEAND MAINTAINING SAID REACTION AT A TEMPERATURE OF ABOUT 985*F. TO 1015*FFOR A PERIOD OF TIME RANGING FROM ABOUT2 HOURS TO 6.5 HOURS AT A PRESUREBETWEEN ABOUT 2000 P. S. I. G. TO 3000 P. S. I. G. DURING SAID RACTIONAND RECOVERING A DESULFURIZED PETROLEUM COKE HAVING A SULFUR CONTENT OFABOUT 1.3 WEIGHT PERCENT OF SULFUR OF LESS.